19 
FIRST AND SECOND INSPECTIONS COMPARED 
Comparing next the conditions found May 28 and June 21, we find 
that the number of hills infested in the check had increased between 
these dates from 57 percent to Th percent for ants, and from 53 per- 
cent to ITi percent for the aphids ; while the number of ants to the 
hill had diminished from 66 to 39 and the number of aphids to the 
hill had increased from 23 to 166. The number of the aphids, it will 
be seen, had increased sevenfold. 
Rate of increase of root-lice in the field. — The period of active 
multiplication of the root-aphis in the field commonly continues until 
early October, approximately six times the period within which we 
found a sevenfold increase. If this rate of increase were maintained 
until the end of the season, the 124,000 aphids per acre found May 28 
would multiply by October 1 to more than 14,340,000,000, or 39,000 to 
the hill of corn. This computation of the actual rate of multiplication 
of the corn root-aphis in the field is sufficient to account completely for 
any amount of injury which these insects may do to the crop under 
conditions favorable to their increase. 
RESULTS OF THE EXPERIMENT. THIRD INSPECTION 
On the 17th of July Mr. Kelly reported a conspicuous difference 
in height between the corn on the experimental strips and that on the 
checks — a difference so great, indeed, that as one looked across the 
field, it seemed to lie in alternate ridges and hollows, the ridges corre- 
sponding to the experimental strips and the hollows to the checks. The 
ground being perfectly level, these differences were evidently due to 
the more rapid growth of the corn in the experimental plots ; or, more 
correctly speaking, to an arrest of growth in the checks resulting from 
the greater drain of insect injury where the corn had not been pro- 
tected by a previous treatment of the seed. Visiting this field July 21, 
I noticed that the central rows of the check strips were shortest, and 
the central rows of the experimental strips were tallest, the transition 
from one to the other being gradual. On passing down a central 
check row, the highest stalks reached, on the average, to my elbows ; 
and on walking down the central row of an experimental strip, the 
tallest stalks were found to reach nearly to the top of my head. 
To verify this observation, measurements were made of the tallest 
stalks in 214 hills of one of the checks, and in 157 hills of the carbolic 
acid plot. The first of these averaged 36 inches and the second 62 
inches. The height of the corn in the check strip was less by 42 per- 
cent than that in the experimental plot, and this was the measure of 
an injury by insects in the former which had been prevented in the 
latter by the treatment of the seed This striking difference was quite 
as obvious to the eye August 27, after all the corn had tasseled. 
RESULTS OF THE EXPERIMENT. FOURTH INSPECTION 
What proved to be a final inspection of this field was made Sep- 
tember 20, when the hills and both fertile and barren stalks were 
